Yes duvets can be reused BUT with great difficulty.
REUSE
We would encourage you to reduce your need to buy a new one by having your duvet cleaned. There are plenty of specialist duvet cleaning companies who can clean your duvet to a high standard and most launderettes have a duvet cleaning service.
If your duvet is in good condition you can sell it at a car boot sale or use a number of online platforms including Gumtree, Friday-Ad, Facebook selling pages, etc.
You can also give it away for free through Freegle.
RSPCA Brighton will take synthetic ones (any size) but not too many at once so please phone ahead and see if they are in need: 01273 554218.
DID YOU KNOW?
Duvets are not accepted by the textiles recycling industry and therefore can not be recycled making it more important to prolong the life of the one you have.